Usage:
Chadron Formation (CO)
Chadron Formation of White River Group (CO*,MT*,NE*,ND*,SD*,WY*)
Subunits:
(alphabetical): Ahearn Member (SD), Beaver Divide Conglomerate Member (WY), Chalky Buttes Member (ND), Crazy Johnson Member (SD), Peanut Peak Member (SD), South Heart Member (ND).
Geologic age:
early Tertiary (late Eocene or early Oligocene)*
Type section, locality, area and/or origin of name:
Not designated. Named from exposures at Chadron, Dawes Co., NE (Darton, 1899, 1931).
Standard [Principal reference] section: in Big Badlands, south fork of Indian Creek, from sec. 34, T. 3 S., R. 12 E., to sec. 10, T. 4 S., R. 12 E., Pennington Co., SD (Clark, 1954).
AAPG geologic province:
Chadron arch*
Denver basin*
Williston basin*
Sioux uplift*
Wind River basin
Green River basin
For more information, please contact Nancy Stamm, Geologic Names Committee Secretary.
Asterisk (*) indicates published by U.S. Geological Survey authors.
"No current usage" (†) implies that a name has been abandoned or has fallen into disuse. Former usage and, if known, replacement name given in parentheses ( ).
Slash (/) indicates name conflicts with nomenclatural guidelines (CSN, 1933; ACSN, 1961, 1970; NACSN, 1983, 2005, 2021). May be explained within brackets ([ ]).